A byproduct of the process for making so-called Greek yogurt, also referred to as “strained yogurt,” is a whey having a relatively high concentration of lactic acid. The increased lactic acid content is due to the fermentation of lactose by bacterial cultures used to make yogurt. Lactic acid concentrations from about 5 weight % (wt. %) dry basis to as much as about 13 wt. % dry basis (% DB) can typically be found in Greek yogurt whey. Because of the relatively high concentration of lactic acid present, whey from Greek yogurt production is often referred to as “acid whey” to distinguish it from other wheys that can result from cheese making. Wheys without the elevated levels of acid are typically referred to as “sweet whey.” Acid whey can also have a lower concentration of lactose compared to sweet whey because a portion of the lactose is converted to lactic acid in the yogurt making process. For example, acid whey can have a lactose concentration of about 60% DB versus about 70% DB for sweet whey. Typically, acid whey also has a relatively low concentration of protein, e.g., as low as 0.3 wt. % protein and as low as 6% DB when compared to sweet whey which typically has about 12 to 13 wt. % protein. Acid whey from Greek yogurt can often also include elevated levels of galactose, e.g. 5 wt. % or more galactose, a component resulting from the enzymatic breakdown of lactose to glucose and galactose.
In order to preserve various types of whey, it can be desirable to remove most of the moisture to form a dry powder. A particularly desirable product is a so-called “free-flowing” powder. The relatively high lactic acid content, the relatively low lactose content, the relatively low protein content and the relatively high galactose content can make acid whey difficult to dry into a free-flowing powder. Both lactic acid and galactose are hygroscopic and can make the drying of acid whey difficult using traditional whey drying equipment. Both lactose (in its monohydrate form) and high molecular weight proteins are non-hygroscopic and aid in the drying of sweet wheys. Therefore, the reduced concentration of lactose monohydrate and the reduced concentration of high molecular weight proteins in acid whey further complicate the drying of acid whey.
Systems and methods for drying various whey compositions are described in the following patents and patent applications: International Application No. WO 86/03942, published on Jul. 17, 1986 and filed on Dec. 19, 1985; Nassauer et al., U.S. Pat. No. 5,580,592, issued on Dec. 3, 1996; Nassauer et al., EP Patent No. EP0619075B1, granted on Jan. 29, 1997; Getler et al., U.S. Pat. No. 5,773,061, issued on Jun. 30, 1998; Getler et al., U.S. Pat. No. 6,048,565, issued on Apr. 11, 2000; Peters et al., U.S. Pat. No. 6,335,045, issued on Jan. 1, 2002; Benningfield et al., U.S. Pat. No. 6,790,288, issued on Sept. 14, 2004; Keller, U.S. Pat. No. 7,241,465, issued on Jul. 10, 2007; Bonke, U.S. Published Application No. 2008/0230051, published on Sep. 25, 2008 and filed on Mar. 27, 2008; the entire disclosures of all of which are incorporated herein by reference.